The present invention generally relates to a method and apparatus for a balloon expandable stent-graft delivery system. More particularly, the present invention relates to a method and apparatus for introducing and securing a stent-graft assembly within a blood vessel using a balloon catheter which allows for the uniform radial expansion of the stent-graft assembly.
Clinical trials have demonstrated the effectiveness and safety of stents for recanalization of obstructed or completely occluded blood vessels. Palmaz, et al., "Stenting of the iliac arteries with the Palmaz stent: Experience from a multicenter trial." 15 Cardiovascular Interventional Radiology 291 (1992); Carrasco, et al., "Use of the Gianturco self-expanding stent in stenoses of the superior and inferior venae cavae." 3 Journal of Vascular and International Radiology 409 (1992). Stents are generally introduced into a blood vessel by the use of a catheter.
Several balloon catheter systems for introducing and delivering a stent into a blood vessel are known in the field of art relating to stents. For example, U.S. Pat. No. 5,108,416 discloses a stent introducer system comprising a balloon catheter having a stent surrounding the balloon portion of the catheter. Flexible end caps having mounting sleeves are affixed to the catheter adjacent the ends of the balloon to retain the stent in its position during inflation of the balloon. Inflation of the balloon causes the end caps to move axially and radially away from the stent, thereby releasing the stent. Another stent delivery system, described in U.S. Pat. No. 4,950,227, includes a catheter having an expandable distal portion, a stent positioned around the distal portion, and an expandable sleeve positioned around the catheter having one end affixed to the catheter and the other end overlapping the stent. Expanding the distal portion of the catheter causes the stent to expand and the sleeve to slide axially away from the stent thereby releasing the stent.
The use of stents in combination with polytetrafluoroethylene (PTFE) or polymer grafts are particularly useful in treating focal vascular lesions such as aneurysms, pseudoaneurysms and arteriovenous fistulas and atherosclerotic and occlusive diseases with both discrete and diffuse lesions by functioning to exclude the abnormal vascular lumen. A PTFE graft is radially expandable if a coaxial balloon is inflated within its lumen. However, physical problems arise when expanding a stent-PTFE graft assembly with a balloon catheter where the PTFE graft material is co-axially placed over the stent.
The length of the balloon chosen for expanding the stent-graft assembly is critical. If an excessively long balloon is chosen, the inflation of the balloon will result in a "dumb-bell" shaped expansion. The "dumb-bell" shaped expansion causes the ends of the stent to flare outward thereby causing the graft to compress in a longitudinal direction and bunch up in the middle of the stent.
Ideally, prior studies have indicated that the balloon length should be less than the length of the stent-graft assembly and have short tapered ends. This shorter balloon expands the stent-graft from the center out and produces an expanded stent-graft assembly with tapered ends. The balloon is then deflated, repositioned, and reinflated to expand the tapered ends of the partially expanded stent-graft assembly. However, this procedure could lead to balloon ruptures or snags due to a lack of uniform and continuous expansion and the need to reposition the balloon to obtain a uniform expansion of the stent-graft assembly.
Further, if used for expanding a stent-graft assembly, the balloon catheter systems for introducing and delivering stents which are currently known would not overcome the physical expansion problems involved in expanding the stent-graft assembly. More specifically, with reference to U.S. Pat. Nos. 5,108,416 and 4,950,227, described above, the end caps and expandable sleeves which would overlap the ends of the stent-graft assembly during the expansion process would produce an expanded stent-graft assembly having tapered ends. These tapered ends would then require additional expansion in order to obtain an expanded stent-graft assembly having a uniform geometry.
Accordingly, there is a need for a method and apparatus for introducing and delivering a stent-graft assembly which is capable of performing a uniform and continuous radial expansion of the stent-graft assembly. There is also a need for a method and apparatus for introducing and delivering a stent-graft assembly which is capable of expanding the stent-graft assembly without incurring substantial retraction of the graft over the stent.